The present invention relates generally to a work-feed mechanism for a sewing machine having a feed dog which is operable to effect four-motion movements to feed a workpiece or workpieces in cooperation with a presser foot. More particularly, the invention is concerned with such a work-feed mechanism having a lower feed needle which is operated in timed relation with the feed dog.
In the art of such type of work-feed mechanism, a work-feed device is known, wherein a lower feed needle is attached to a feed dog. However, this device suffers a problem when a workpiece to be sewn is relatively thick. To solve this problem, there has been proposed a device which is disclosed in TOKU-KAI-SHO 57-166194 (Japanese patent application laid open Oct. 13, 1982 under Publication No. 57-166194), wherein a feed bar carrying a feed dog is provided with a lower feed needle which is movable relative to the feed dog. A movement to the lower feed needle is imparted from a feed-lift mechanism (for imparting a vertical movement to the feed dog) via plural pivotable levers provided on the feed bar. This arrangement makes it possible to obtain a vertical displacement of the lower feed needle larger than that of the feed dog, thus effectively preventing a relative horizontal displacement between the opposite surfaces of a workpiece or superposed workpieces even when the total thickness of the workpiece(s) is large.
However, the proposed work-feed device referred to just above still suffers a problem. That is, a linkage for imparting the relative movements to the lower feed needle uses a large number of parts, and the linkage is connected to the feed-lift mechanism to give said relative movements to the lower feed needle. Such linkage arrangement of the proposed work-feed device requires a considerable degree of modification of the feed-lift mechanism of a sewing machine, to provide the machine with such a work-feed device.